Cementitious blend and concrete mix compositions resistant to high temperatures and alkaline conditions

ABSTRACT

A cementitious blend composition and a concrete mix composition preferable for making concrete resistant to high temperatures and alkaline conditions, particularly for making durable concrete for constructing an alumina digester tank in an aluminum smelter. The cementitious blend composition includes at least one hydraulic cement, silica fume (SF), and natural pozzolan (NP), wherein a weight percent ratio of at least one hydraulic cement: SF:NP in the cementitious blend composition lies in the range of (24-63): (5-44): (32-40) with the sum of the weight percentages of the at least one hydraulic cement, the SF, and the NP not exceeding 100%. The concrete mix composition comprises water and the cementitious blend composition, wherein a weight ratio of the water the cementitious blend composition is 0.2-0.5, and wherein the concrete mix composition has a content of the cementitious blend composition of 400-550 kg/m 3 .

BACKGROUND OF THE INVENTION Technical Field

The present disclosure relates to cementitious blend and concrete mixcompositions resistant to high temperatures and alkaline conditions,particularly for making durable concrete for constructing an aluminadigester tank resistant to a hot caustic soda solution.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, is neitherexpressly nor impliedly admitted as prior art against the presentinvention.

In North American practice, high strength concrete is usually consideredto be concrete with a 28-day compressive strength of at least 42 MPa.Compared with conventional concrete, high strength concrete is moredurable because of reduced porosity, inhomogeneniety, and microcracks.

It is an object of the present disclosure to provide cementitious blendand concrete mix compositions for making high strength, durable concreteresistant to high temperatures and alkaline conditions that is, forexample, suited for constructing an alumina digester tank in an aluminumsmelter. Preferred embodiments of the cementitious blend and concretemix compositions use both hydraulic cements and supplementarycementitious materials, such as silica fume (SF), ground granulatedblast furnace slag (GGBFS), and naturual pozzolan (NP). Since most ofthe supplementary cementitious materials are industrial by-products, theuse of the supplementary cementitious materials in the inventivecompositions helps reduce the amount of hydraulic cements required tomake the resultant concrete less costly, more environmentally friendly,and less energy intensive.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to acementitious blend composition that includes at least one hydrauliccement, silica fume (SF), and natural pozzolan (NP), wherein a weightpercent ratio of at least one hydraulic cement: SF:NP in thecementitious blend composition lies in the range of (24-63): (5-44):(32-40) with the sum of the weight percentages of the at least onehydraulic cement, the SF, and the NP not exceeding 100%.

In one or more embodiments, the at least one hydraulic cement is atleast one selected from the group consisting of a Portland cement, acalcium aluminate cement, a white cement, a high-alumina cement, amagnesium silicate cement, a magnesium oxychloride cement, and an oilwell cement.

In one or more embodiments, the natural pozzolan (NP) is at least oneselected from the group consisting of metakaolin, calcined shale,calcined clay, volcanic glass, zeolitic trass or tuffs, rice husk ash,Diatomaceous earth, and calcined shale.

In one or more embodiments, the present disclosure relates to a concretemix composition comprising water and the cementitious blend composition,wherein a weight ratio of the water to the cementitious blendcomposition is 0.2-0.5, and wherein the concrete mix composition has acontent of the cementitious blend composition of 400-550 kg/m³.

In one or more embodiments, the concrete mix composition furthercomprises at least one reinforcing material selected from the groupconsisting of steel rebar, wire mesh, steel fibers, polypropylenefibers, nylon fibers, and polyvinyl alcohol fibers.

In one or more embodiments, the concrete mix composition furthercomprises at least one high range water reducer.

In one or more embodiments, the at least one high range water reducer isa polycarboxylate superplasticizer or a naphthalene high range waterreducer.

In one or more embodiments, the present disclosure relates to an aluminadigester tank system that includes (a) an alumina digester tank obtainedfrom a casting or molding of the concrete mix composition in the form ofthe alumina digester tank and water curing the cast or molded concretemix composition, wherein the alumina digester tank has a height todiameter ratio of 1-5 and comprises a top wall, a bottom wall, and sidewalls defining an enclosed space, (b) at least one inlet disposed on atleast one of the top wall, the bottom wall, and the side walls of thealumina digester tank configured to introduce a mixture comprisingbauxite and a caustic soda solution into the enclosed space of thealumina digester tank, wherein the alumina digester tank is configuredto pressurize the mixture in the enclosed space to 1-100 bars, (c) atleast one heater disposed on the interior of at least one of the topwall, the bottom wall, and the side walls and/or in the enclosed spaceof the alumina digester tank configured to heat the mixture to atemperature of 60-300° C., (d) at least one outlet disposed on at leastone of the top wall, the bottom wall, and the side walls configured torelease the mixture from the enclosed space of the alumina digestertank, (e) at least one agitator disposed on the interior of at least oneof the top wall, the bottom wall, and the side walls and/or in theenclosed space of the alumina digester tank configured to agitate themixture in the enclosed space, (f) a temperature detector for detectingthe temperature of the mixture in the enclosed space of the aluminadigester tank, (g) a pressure detector for detecting the pressureapplied to the mixture in the enclosed space of the alumina digestertank, and (h) a control for operating the at least one heater, whereinthe control is configured to monitor the temperature of the mixture inthe enclosed space of the alumina digester tank and operate he at leastone heater when the temperature of the mixture is below a pre-determinedlevel.

In one or more embodiments, the alumina digester tank system furthercomprises at least one first pump connected to the at least one inletconfigured to pump the mixture into the enclosed space of the aluminadigester tank via the at least one inlet, at least one second pumpconnected to the at least one outlet configured to pump the mixture outof the enclosed space of the alumina digester tank via the at least oneoutlet, and at least one baffle disposed on the interior of at least oneof the top wall, the bottom wall, and the side wails and/or in theenclosed space of the alumina digester tank configured to achieve adesired flow pattern of the mixture in the enclosed space of the aluminadigester tank.

In one or more embodiments, a surface of the interior of at least one ofthe top wall, the bottom wall, and the side walls of the aluminadigester tank of the alumina digester tank system is coated with atleast one epoxy resin.

In one or more embodiments, the at least one hydraulic cement of theconcrete mix composition is a Portland cement.

In one or more embodiments, the at least one hydraulic cement of theconcrete mix composition is a Portland cement, and the water curedproduct of the concrete mix composition has a compressive strength of60-90 MPa.

In one or more embodiments, the at least one hydraulic cement of theconcrete mix composition is a Portland cement, and the water curedproduct of the concrete mix composition has a reduction in compressivestrength of 2-15% when exposed to an alkaline solution comprising 10-50%of one or more alkali hydroxides at 40-80° C. for 4-16 months ascompared to the water cured product of the concrete mix compositionexposed to water at 15-35° C. for the same length of time.

In one or more embodiments, the at least one hydraulic cement of theconcrete mix composition is a Portland cement, and the water curedproduct of the concrete mix composition has a weight loss of 0-6% whenexposed to an alkaline solution comprising 10-50% of one or more alkalihydroxides at 40-80° C. for 4-16 months as compared to the water curedproduct of the concrete mix composition exposed to water at 15-35° C.for the same length of time.

In one or more embodiments, the at least one hydraulic cement of theconcrete mix composition is a Portland cement, and the water curedproduct of the concrete mix composition has a chloride permeability of1200-2000 Coulombs when exposed to an alkaline solution comprising10-50% of one or more alkali hydroxides at 40-80° C. for 12-16 months.

In one or more embodiments, the at least one hydraulic cement of theconcrete mix composition is a Portland cement, and the water curedproduct of the concrete mix composition has an expansion of 200-850microns when exposed to an alkaline solution comprising 10-50% of one ormore alkali hydroxides at 40-80° C. for 4-16 months.

In one or more embodiments, the concrete mix composition furthercomprises at least one aggregate selected from the group consisting offused aluminum oxide (FAO), calcined bauxite, and emery.

In one or more embodiments, the at least one aggregate comprises fusedaluminum oxide (FAO) at 50-100% of the total volume of the at least oneaggregate.

According to a second aspect, the present disclosure relates to analumina digester tank system that includes (a) an alumina digester tankobtained from a casting or molding of a concrete mix composition in theform of the alumina digester tank and water curing the cast or moldedconcrete mix composition, wherein the alumina digester tank has a heightto diameter ratio of 1-5 and comprises a top wall, a bottom wall, andside walls defining an enclosed space, wherein the concrete mixcomposition comprises: a cementitious blend comprising at least onehydraulic cement and ground granulated blast furnace slags (GGBFS),wherein a weight percent ratio of at least one hydraulic cement: GGBFSin the cementitious blend lies in the range of (10-50): (50-90) with thesum of the weight percentages of the at least one hydraulic cement andthe GGBFS not exceeding 100%, and water, wherein a weight ratio of thewater to the cementitious blend is 0.2-0.5, and wherein the concrete mixcomposition has a content of the cementitious blend of 400-550 kg/m³,(b) at least one inlet disposed on at least one of the top wall, thebottom wall, and the side walls of the alumina digester tank configuredto introduce a mixture comprising bauxite and a caustic soda solutioninto the enclosed space of the alumina digester tank, wherein thealumina digester tank is configured to pressurize the mixture in theenclosed space to 1-100 bars, (c) at least one heater disposed on theinterior of at least one of the top wall, the bottom wall, and the sidewalls and/or in the enclosed space of the alumina digester tankconfigured to heat the mixture to a temperature of 60-300° C., (d) atleast one outlet disposed on at least one of the top wall, the bottomall, and the side walls of the alumina digester tank configured torelease the mixture from enclosed space of the alumina digester tank,(e) at least one agitator disposed on the interior of at least one ofthe top wall, the bottom wall, and the side walls and/or in the enclosedspace of the alumina digester tank configured to agitate the mixture inthe enclosed space, (f) a temperature detector for detecting thetemperature of the mixture in the enclosed space of the alumina digestertank, (g) a pressure detector for detecting the pressure applied to themixture in the enclosed space of the alumina digester tank, and (h) acontrol for operating the at least one heater, wherein the control isconfigured to monitor the temperature of the mixture in the enclosedspace of the alumina digester tank and operate the at least one heaterwhen the temperature of the mixture is below a pre-determined level.

In one or more embodiments, a surface of the interior of at least one ofthe top wall, the bottom wall, and the side walls of the aluminadigester tank of the alumina digester tank system is coated with atleast one epoxy resin.

The foregoing paragraphs have been provided by way of generalintroduction,and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is a picture showing the condition of concrete mix specimen M1following an exposure to a caustic soda solution for 16 months accordingto Example 3.

FIG. 19 is a picture showing the condition of concrete mix specimen M1following an exposure to potable water for 16 months according toExample 3.

FIG. 2A is a picture showing the condition of concrete mix specimen M2following an exposure to a caustic soda solution for 16 months accordingto Example 3.

FIG. 2B is a picture showing the condition of concrete mix specimen M2following an exposure to potable water for 16 months according toExample 3.

FIG. 3A is a picture showing the condition of concrete mix specimen M3following an exposure to a caustic soda solution for 16 months accordingto Example 3.

FIG. 3B is a picture showing the condition of concrete mix specimen M3following an exposure to potable water for 16 months according toExample 3.

FIG. 4A is a picture showing the condition of concrete mix specimen M4following an exposure to a caustic soda solution for 16 months accordingto Example 3.

FIG. 4B is a picture showing the condition of concrete mix specimen M4following an exposure to potable water for 16 months according toExample 3.

FIG. 5 is a graphical presentation of compressive strength of concretemix specimens M1-M4 with increasing curing time in water up to threemonths according to Example 3.

FIG. 6 is a graphical presentation of reduction in compressive strengthof concrete mix specimens M1-M4 following an exposure to a caustic sodasolution (320 g/L NaOH) at 60° C. for 4, 8, 12, or 16 months as comparedto concrete mix specimens M1-M4 exposed to water at 23±2° C. for thesame length of time according to Example 3.

FIG. 7 is a graphical presentation of weight loss of concrete mixspecimens M1-M4 following an exposure to a caustic soda solution (320g/L NaOH) at 60° C. for 4, 8, 12, or 16 months as compared to concretemix specimens M1-M4 exposed to water at 23±2° C. for the same length oftime according to Example 3.

FIG. 8 is a graphical presentation of chloride permeability in concretemix specimens M1-M4 unexposed or exposed to a caustic soda solution (320g/L NaOH) at 60° C. for 12 or 16 months according to Example 3.

FIG. 9 is a graphical presentation of expansion in concrete mixspecimens M1-M4 following an exposure to a caustic soda solution (320g/L NaOH) at 60° C. for 4, 8, 12, or 16 months according to Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to a first aspect, the present disclosure relates to acementitious blend composition preferably for making concrete resistantto high temperatures, e.g. 60-300° C., 80-300° C., 100-300° C., 100-250°C., 120-200° C., or 150-180° C., and alkaline conditions, morepreferably for making durable concrete for constructing an aluminadigester tank in an aluminum smelter. The cementitious blend compositionincludes at least one hydraulic cement, silica fume (SF), and naturalpozzolan (NP), wherein a weight percent ratio of at least one hydrauliccement: SF:NP in the cementitious blend composition lies in the range of(25-70): (5-20) : (25-55), (24-63): (5-44): (32-40), or (30-55): (5-40): (30-40), with the sum of the weight percentages of the at least onehydraulic cement, the SF, and the NP not exceeding 100%.

In some embodiments, the cementitious blend composition does not includefly ash, or GGBFS, or a combination of fly ash and GGBFS.

In one embodiment, the cementitious blend composition is combined withwater to obtain a concrete mix composition, wherein a weight ratio ofthe water to the cementitious blend composition is 0.2-0.5, 0.3-0.4, or0.35, and wherein the concrete mix composition has a content of thecementitious blend composition of 400-550 kg/m³, 400-500 kg/m³, 405-480kg/m³, 430-470 kg/m³, or 460 kg/m³.

Hydraulic cements set and become adhesive due to a chemical reactionbetween the dry ingredients and water. The chemical reaction results inmineral hydrates that are not very water-soluble and so are quitedurable in water and safe from chemical attack. This allows setting inwet conditions or underwater and further protects the hardened materialfrom chemical attack.

In one embodiment, the hydraulic cement is a Portland cement. In apreferred embodiment, the Portland cement meets ASTM C150 Type I, II,I/II, III, IV or V requirements or equivalent standard specifications.

Portland cement is by far the most common type of cement in general usearound the world. This cement is made by heating limestone (calciumcarbonate) with other materials (such as clay) to 1450° C. in a kiln, ina process known as calcination, whereby a molecule of carbon dioxide isliberated from the calcium carbonate to form calcium oxide, orquicklime, which is then blended with the other materials that have beenincluded in the mix to form calcium silicates and other cementitiouscompounds. The resulting hard substance, called ‘clinker’, is thenground with a small amount of gypsum into a powder to make “OrdinaryPortland Cement”, the most commonly used type of cement (often referredto as OPC). Portland cement s a basic ingredient of concrete, mortar andmost non-specialty grout. The most common use for Portland cement is inthe production of concrete. Concrete is a composite material typicallycomprising aggregate (gravel and sand), cement, and water. As aconstruction material, concrete can be cast in almost any shape desired,and once hardened, can become a structural (load bearing) element.Portland cement reacts with water to form primarily calcium silicatehydrate. The strength of the resultant concrete results from a hydrationreaction between the silicate phases of Portland cement and water toform calcium silicate hydrate Ca₃Si₂O₁₁H₈ (3CaO.2SiO₂.4H₂O, or C₃S₂H₄ inCement chemist notation (CCN)) and calcium hydroxide (lime) as aby-product.

In another embodiment, the hydraulic cements a calcium aluminate cementthat advantageously provides resistance to a high temperature, e.g.900-1600° C., 1000-1500° C., or 1200-1300° C., depending on theparticular concrete composition. Calcium aluminate cements are madeprimarily from limestone and bauxite. The active ingredients aremonocalcium aluminate CaAl₂O₄ (CaO.Al₂O₃ or “CA” in CCN) and magnetiteCa₁₂Al₁₄O₃₃ (12CaO.7Al₂O₃, or C₁₂A₇ in CCN). Strength of the resultantconcrete results from hydration to calcium aluminate hydrates.

In another embodiment, the hydraulic cement is one or more cementsselected from the group consisting of a Portland cement, a calciumaluminate cement, a white cement, a high-alumina cement, a magnesiumsilicate cement, a magnesium oxychloride cement, and an oil well cement(e.g., Type VI, VII and VIII). When the hydraulic cement is a mixture ofthe above mentioned cements, the relative weight proportions ofdifferent types of cements may vary without limitation, depending on,for example, the desired content of the cementitious blend compositionin the concrete mix composition, which is preferably within the rangesdescribed above, the desired compressive strength of the resultantconcrete from the concrete mix composition after a certain period ofcuring of the concrete mix composition with water, and a target (high)temperature the resultant concrete is expected to withstand and remainstable, e.g. without breaking or cracking, for a desirable period oftime.

Relative to the hydraulic cement, the silica fume and natural pozzolanin the cementitious blend composition are supplementary cementitiousmaterials that advantageously reduce the costs of the cementitious blendcomposition and improve the durability and strength of the resultantconcrete from the concrete mix composition comprising the cementitiousblend composition, particularly in a hot and alkaline environment, suchas that in an operating alumina digester tank containing a NaOH (causticsoda) solution at a temperature of 60-300° C., 80-300° C., 100-300° C.,100-250° C., 120-200° C., or 150-180° C. The silica fume and naturalpozzolan react with calcium hydroxide, a by-product of Portland cementhydration to form additional binder conferring increased durability andstrength. The concrete formed from a concrete mix composition comprisingcalcium aluminate cement, silica fume, and natural pozzolan likewise hasincreased durability and strength due to prevention or reduction ofconversion (a change in the internal structure of the concrete).

Silica fume, also known as microsilica, is an amorphous(non-crystalline) polymorph of silicon dioxide, or silica. It is anultrafine powder collected as a by-product of the silicon andferrosilicon alloy production and comprises spherical particles with anaverage particle diameter of 100-1000 nm, 200-800 nm, 300-600 nm, or400-500 nm. The main field of application of silica fume is aspozzolanic material for high performance concrete. Preferable standardspecifications for silica fume used in the cementitious blendcomposition are ASTM C1240.

Pozzolans are a broad class of siliceous or siliceous and aluminonsmaterials which, in themselves, possess little or no cementitious valuebut which will, in finely divided form and in the presence of water,react chemically with calcium hydroxide at ordinary temperature to formcompounds possessing cementitious properties.

Pozzolans encompass a large number of materials. Non-limiting examplesof natural pozzolan include metakaolin, calcined shale, calcined clay,volcanic glass, zeolitic trass or tuffs, rice husk ash, Diatomaceousearth, and calcined shale. In a preferred embodiment, the naturalpozzolan meets the standard specification ASTM C618.

In the concrete mix composition, in some embodiments, the content of theat least one hydraulic cement is 120-300 kg/m³, 150-280 kg/m³, 180-260kg/m³, or 200-250 kg/m³; the content of the silica fume (SF) is 20-310kg/m³, 50-280 kg/m³, 80-250 kg/m³, 110-220 kg/m³, or 140-190 kg/m³; andthe content of the natural pozzolan (NP) is 120-220 kg/m³, 140-200kg/m³, or 160-180 kg/m³, with the combined content of the hydrauliccement, the SF, and the NP at 400-550 kg/m³, 400-500 kg/m³, 405-480kg/m³, 430-470 kg/m³, or 460 kg/m³.

In one embodiment, the concrete mix composition further comprisesaggregates, e.g. gravel and/or sand. Aggregates preferably make up about60 to 80 percent of the total volume of the concrete mix composition, or70-85% of the total weight of the concrete mix composition. Theaggregates may be coarse aggregates, fine aggregates, or a mixture ofcoarse aggregates and fine aggregates. Coarse aggregate is usuallygreater than 4.75 mm (retained on a No. 4 sieve), e.g. 5-20 mm, 8-18 mm,10-15 mm, or 12-14 min, while fine aggregate is less than 4.75 mm(passing the No. 4 sieve), e.g. 0.1-4.5 mm, 0.2-4 mm, 0.5-3 mm, or 1-2mm. In a preferred embodiment, the aggregates are at least one selectedfrom the group consisting of fused aluminum oxide (FAO), calcinedbauxite, and emery to make the resultant concrete from the concrete mixcomposition resistant to high temperatures. In another preferredembodiment, the aggregates comprise fused aluminum oxide (FAO) at50-100%, 60-90%, or 70-80% of the total volume of the aggregates. FAQ isa refractory material and has a linear coefficient of thermal expansionof 5.4×10⁻⁶m/m*° C., which is significantly less than siliceous sands(e.g., fine sand and quartz). At a temperature of 572.7° C., FAO expands0.85% as described in American Society for Testing and Materials (ASTM)STP169C, entitled “Significance of Tests and Properties of Concrete andConcrete-Making Materials”, incorporated herein by reference in itsentirety. FAO expands and contracts considerably less in response tohigh temperatures than siliceous sands. Excessive expansion of theaggregate degrades the structural integrity of a concrete due to thedevelopment of high internal tensile stresses in the concrete.Therefore, the use of FAO as an aggregate provides a measure of heatresistance to a concrete in which it is carried compared with a concretecontaining only siliceous sands.

To provide additional resistance to high temperatures and alkalineconditions, in a preferred embodiment, a surface of the resultantconcrete from the concrete mix composition is coated with an epoxy resinor a mixture of epoxy resins. The epoxy resin coating is preferably awaterborne epoxy resin coating, more preferably a high performancewaterborne epoxy resin coating for concrete disclosed in Chinese PatentNo. CN104710899 A, incorporated herein by reference in its entirety. Inother embodiments, the epoxy resin coating comprises at least one epoxyresin selected from the group consisting of bisphenol A, bisphenol F,epichlorohydrin, and tetraglycidyldiaminodiphenylmethane. In oneembodiment, the epoxy resin coating may be applied on the surface of theconcrete by mixing the epoxy resin with a curing agent and silica sandand then spreading the mixture over the concrete surface followed bypress-forming plastering using a finisher. The resins used preferablyhave good flowability with an intermediate level of viscosity to be wellmixed with silica sand and also provide easier press-forming plastering.In a preferred embodiment, the surface of the concrete is treated with amultifunctional primer adhesive before the mixture of epoxy resin, acuring agent, and silica sand is applied on the adhesive-treatedconcrete surface, as disclosed in International Application PublicationNo. WO2005063880 A1, incorporated herein by reference in its entirety.In some embodiments, the epoxy resin coating has a thickness of 0.1-1mm, 0.2-0.8 mm, 0.3-0.6 rum, 1-10 mm, 2-8 mm, or 3-5 mm.

In another embodiment, the concrete mix composition may be mixed withone or more epoxy resins (and their curing agents or hardners if needed)to form a concrete with cured epoxy resin particles dispersed throughoutthe mass of the concrete. Such a concrete may possess improved tensilestrength and chemical resistance. The amount of the epoxy resins or thetotal amount of the epoxy resins and their curing agents used inpreparing the mixture for making the epoxy resin incorporated concretemay vary depending on the strength of the concrete desired and economicconsiderations. Generally, the amount of the epoxy resins or the epoxyresins plus the curing agents is 0.5-20%, 1-10%, 3-8%, or 4-6% of thetotal weight of the concrete mix composition, which may include theweight of aggregates when aggregates are included in the concrete mixcomposition.

Besides the epoxy resins described above, other suitable epoxy resinsfor making the epoxy resin incorporated concrete include a polyepoxidethat possesses more than one vic-epoxy (oxirane) group per molecule andthat may be saturated or unsaturated, aliphatic, cycloaliphatic,aromatic or heterocyclic, as disclosed in U.S. Pat. No. 3,477,979 A,incorporated herein by reference in its entirety, and diglycidyl etherof bisphenol A disclosed in U.S. Pat. No. 3,949,144 A, incorporatedherein by reference in its entirety.

Any suitable and convenient manner and order to mix the materials of theconcrete mix composition and the epoxy resins may be used generally.However, it is desirable and advantageous to prepare the epoxy resin ora mixture of the epoxy resin and the curing agent separately and thenadd it to the concrete mix composition. A mixture for making an epoxyresin incorporated concrete may be prepared as follows:

-   -   1. mix a suitable amount of the cementitious blend composition        of the concrete mix composition with a suitable amount of one or        more epoxy resins (and their curing agents if needed), and    -   2. add water to the mixture of the cementitious blend        composition and the epoxy resins. Stir he resulting mixture to        ensure that the resulting mixture is consistent throughout.

To provide impact resistance to the resultant concrete from the concretemix composition, in a preferred embodiment, the concrete mix compositionfurther comprises one or more reinforcing materials selected from thegroup consisting of steel rebar, wire mesh, steel fibers, polypropylenefibers, nylon fibers, and polyvinyl alcohol fibers. The reinforcingmaterials may provide impact resistance by increasing the flexural andtensile strength of the concrete formed from the concrete mixcomposition and thus increasing the amount of energy required to causerupture and complete failure. Advantageously, the reinforcing materialsprovide strength when cracks form in the concrete, since the reinforcingmaterials bridge the void created by the crack and allow the concrete todeform in a ductile manner. In some embodiments, the total content ofthe reinforcing material is between 0.25% and 2% of the concrete mixcomposition by volume, preferably between 0.6% and 2% of the concretemix composition by volume, and preferably 1, to 2% of the concrete mixcomposition by volume. When additional resistance to high temperaturesis desired, polypropylene fibers and/or polyvinyl alcohol fibers may beused as the reinforcing material. When exposed to high temperatures, thepolypropylene fibers and/or polyvinyl alcohol fibers melt and decompose,opening channels in the concrete. The channels allow water vapour (e.g.,steam), which is generated from the decomposition of hydrated cements,to escape from the concrete, reducing and/or preventing the cracking andspalling of concrete due to generation of high internal tensile forces.There are various ways of making reinforced concrete. Reinforcedconcrete can be made by forming the concrete inside a metal or timberframework or by casting the concrete around ridged steel bars, or rebars(reinforcing bars). Another variation called stressed or prestressedconcrete involves molding wet concrete around pretensioned steel wires.The wires compress the concrete as it sets, making it much harder. Tomake fiber-reinforced concrete mix, reinforcing fibers may be mixed withthe cementitious blend composition, water, and optionally sand andaggregates.

In another preferred embodiment, the concrete mix composition furthercomprises at least one high range water reducer, also known assuperplasticizer. One suitable type of high range water reducer may be apolycarboxylate superplasticizer, e.g. a viscosity-control typepolycarboxylate superplasticizer as disclosed in Chinese PatentApplication Publication No. CN103553413 A, an early-strengthpolycarboxylate superplasticizer as disclosed in Chinese PatentApplication Publication No. CN103011669 A, and an ether polycarboxylatesuperplasticizer as disclosed in Chinese Patent Application PublicationNo. CN104261720 A. Each of the above mentioned Chinese patentapplication publications is incorporated herein by reference in itsentirety. The polycarboxylate superplasticizer included in the concretemix composition preferably meets ASTM 0494 Type F and G requirements.Another suitable type of high range water reducer may be a naphthalenehigh range water reducer, particularly when the hydraulic cement in theconcrete mix composition is a Portland cement, a calcium aluminatecement, or a mixture thereof. Non-limiting examples of suitablenaphthalene high range water reducers include those disclosed in U.S.Pat. Nos. 4,460,720A, 5,858,083, and 4,164,426, and Chinese PatentApplication Publication No. CN 102086105A, each of which is incorporatedherein by reference in its entirety. Additionally, other types ofsuperplasticizers may also be appropriate, such as a sulfonatedcopolymer of styrene and alpha-methylstyrene or a salt thereof disclosedin U.S. Pat. No. 4,746,367A, incorporated herein by reference in itsentirety. A water reducer reduces the water content (e.g., thewater/cementitious blend composition weight ratio), decreases theconcrete porosity, increases the concrete strength as less water isrequired for the concrete to remain workable, increases the workability,reduces the water permeability (due to a reduction in connectedporosity), and reduces the diffusivity of aggressive agents in theconcrete and thereby improves the durability of the concrete. A highrange water reducer is an admixture which has the ability to reduce theamount of water over a wide range, for example, 5 to 15% as per ASTM0494 while maintaining a certain level of consistency and workability,as compared with conventional water reducers with a narrower range of 5to 8%. A typical dosage of high range water reducers used for increasingthe workability of concrete ranges from 1 to 3 liters per cubic meter ofconcrete where liquid high range water reducers contain about 40% ofactive material. In reducing the water/cementitious blend compositionweight ratio, a higher dosage may be used, e.g. from 5 to 20 liters percubic meter of concrete. Dosage needed for a specific concrete may beunique and may be determined by the Marsh Cone Test.

In some embodiments, the hydraulic cement in the concrete mixcomposition is a Portland cement and, after the concrete mix compositionis cured with water for at least 1 month, at least 2 months, or at least3 months, the water cured product of the concrete mix composition has acompressive strength of 50-110 MPa, 55-100 MPa, or 60-90 MPa.

In some embodiments, the hydraulic cement in the concrete mixcomposition is a Portland cement and, after the concrete mix compositionis cured with water for at least 1 month, at least 2 months, or at least3 months, the water cured product of the concrete mix composition has areduction in compressive strength of 2-15%, 4-10%, or 6-8% when exposedto an alkaline solution comprising 10-50%, 15-45%, 20-40%, or 25-35% ofone or more alkali hydroxides (i.e. LiOH, NaOH, KOH, RbOH, and CsOH) at40-80° C., 50-70° C., or 60° C. for 4-16 months, 6-14 months, 8-12months, or 10 months as compared to the water cured product of theconcrete mix composition exposed to water at 15-35° C., 20-30° C., or25° C. for the same length of time.

In some embodiments, the hydraulic cement in the concrete mixcomposition is a Portland cement and, after the concrete mix compositionis cured with water for at least 1 month, at least 2 months, or at least3 months, the water cured product of the concrete mix composition has aweight loss of 0-6%, 0-4%, 0-2%, 0-1%, or 0-0.5% when exposed to analkaline solution comprising 10-50%, 15-45%, 20-40%, or 25-35% of one ormore alkali hydroxides (i.e. LiOH, NaOH, KOH, RbOH, and CsOH) at 40-80°C., 50-70° C., or 60° C. for 4-16 months, 6-14 months, 8-12 months, or10 months as compared to the water cured product of the concrete mixcomposition exposed to water at 15-35° C., 20-30° C., or 25° C. for thesame length of time.

In some embodiments, the hydraulic cement in the concrete mixcomposition is a Portland cement and, after the concrete mix compositionis cured with water for at least 1 month, at least 2 months, or at least3 months, the water cured product of the concrete mix composition has achloride permeability of 500-2500, 900-2200, 1200-2000, or 1400-1800Coulombs when exposed to an alkaline solution comprising 10-50%, 15-45%,20-40%, or 25-35% of one or more alkali hydroxides (i.e. LiOH, NaOH,KOH, RbOH, and CsOH) at 40-80° C., 50-70° C., or 60° C. for 8-20 months,10-18 months, 12-16 months, or 13-15 months.

In some embodiments, the hydraulic cement in the concrete mixcomposition is a Portland cement and, after the concrete mix compositionis cured with water for at least 1 month, at least 2 months, or at least3 months, the water cured product of the concrete mix composition has anexpansion of 200-850 microns, 250-800 microns, 300-740 microns, 350-700microns, 400-650 microns, 450-600 microns, or 500-550 microns whenexposed to an alkaline solution comprising 10-50%, 15-45%, 20-40%, or25-35% of one or more alkali hydroxides (i.e. LiOH, NaOH, KOH, RbOH, andCsOH) at 40-80° C., 50-70° C., or 60° C. for 4-16 months, 6-14 months,8-12 months, or 10 months.

The void content of a concrete significantly affects its strength.Cement content can be low if the void content is low and vice versa. Insome embodiments, the resultant concretes from the embodiments of theconcrete mix composition have a void content of less than 15% by volume,preferably less than 10% by volume, or more preferably less than 5% byvolume.

Since the resultant concretes from all of the above mentionedembodiments of the concrete mix composition may be resistant to hightemperatures and alkaline solutions, each of the above mentionedembodiments of the concrete mix composition, preferably the embodimentscomprising a Portland cement, a calcium aluminate cement, at least oneaggregate selected from FAO, calcined bauxite, and emery, at least onereinforcing material selected from polypropylene fibers and polyvinylalcohol fibers, and/or a polycarboxylate superplasticizer, may beadvantageously cast or molded in the form of an alumina digester tank inan aluminum smelter and the resultant cast or molded mass is cured withwater to obtain the alumina digester tank made of concrete resistant toa high temperature of, for example, 60-300° C., 80-300° C., 100-300° C.,100-250° C., 120-200° C., or 150-180° C., and a caustic soda (NaOH)solution at a concentration of, for example, 200-600 g/L, 300-500 g/L,or 320-450g/L. As an example, to prepare the concrete mix compositionfor constructing the alumina digester tank according to one embodimentof the concrete mix composition, the aggregates may be mixed first,followed by addition of the hydraulic cement, part of sand if sand isincluded in the mix, and water containing a required amount of a highrange water reducer. The final mixing stage involves the addition ofnatural pozzolan and silica fume, and the remaining sand if sand isincluded in the mix.

When in operation, an alumina digester tank is a high temperature andalkaline environment by the presence of a hot sodium hydroxide (causticsoda) solution. Aluminum production from bauxite ore is a three stepprocess. First, the alumina is extracted from bauxite ore usually usingthe Bayer Process. In the Bayer Process, finely crushed bauxite is mixedwith sodium hydroxide and placed in an alumina digester tank. Hightemperatures (e.g. 60-300° C., 80-300° C., 100-300° C., 100-250° C.,120-200° C., or 150-180° C.) and pressures (from atmospheric pressurefor a gibbsitic bauxite to tens of bars for a diasporic bauxite) in thealumina digester tank cause reactions in the ore/sodium hydroxidemixture that last from 30 minutes to several hours. The result isdissolved aluminum oxide (i.e. sodium aluminate) and ore residues. Theresidues, which include silicon, lead, titanium, and calcium oxides,form a sludge in the bottom of the alumina digester tank. The aluminumoxide is evaporated off and condensed. Starches and other ingredientsare added to remove any remaining impurities from the oxide. Thesolution is then moved to a precipitation tank where the aluminum oxideis crystallized. Aluminum hydroxide and sodium hydrizide are theproducts of the crystallization. The crystals are washed, vacuumdewatered and sent to a calcinator for further dewatering. Aluminumoxide from the Bayer Process is then reduced to aluminum metal usuallyusing the Hall-Heroult process. In this process the aluminum oxide isplaced in a electrolytic cell with molten cryolite. A carbon rod in thecell is charged and the reaction results in carbon monoxide, carbondioxide and aluminum. The aluminum sinks to the bottom where it isremoved from the tank and sent to a melting or holding furnace. Themolten aluminum is then mixed with desired alloys to obtain specificcharacteristics and cast into ingots for transport to fabricating shops.In the fabrication shops, the molten aluminum or aluminum alloys areremelted and poured into casts and cooled. Molten aluminum may befurther heated to remove oxides, impurities and other active metals suchas sodium and magnesium, before casting. Chlorine may also be bubbledthrough the molten aluminum to further remove impurities.

In a preferred embodiment, the alumina digester tank constructed withthe resultant concrete from the concrete mix composition is of acylindrical or similar shape that has a height to diameter ratio of 1-5,2-4, or 3-4. Preferably designed to function as a pressure cooker orvessel to dissolve alumina contained in bauxite in a caustic sodasolution at a high temperature and pressure, the alumina digester tankcomprises a top wall, a bottom wall, and side wails defining an enclosedspace inside the alumina digester tank and is part of an aluminadigester tank system operational in an aluminum production processdescribed above. Besides the alumina digester tank, the alumina digestertank system comprises one or more inlets disposed on at least one of thetop wall, the bottom wall, and the side walls of the alumina digestertank configured to introduce a mixture comprising bauxite and a causticsoda solution into the enclosed space of the alumina digester tank. In apreferred embodiment, the bauxite in the mixture has been ground to finegrains with a diameter of, for example, less than 500 μm, less than 400μm, or less than 300 μm, to increase the contact surface between thecaustic soda solution and the bauxite and to improve the yield of thedigestion, i.e. the solubilization of alumina in the caustic sodasolution. In one embodiment, the inlet is connected to a pump configuredto pump the mixture or slurry of the fine grains of bauxite and thecaustic soda solution into the enclosed space of the alumina digestertank via the inlet.

To increase the digestion efficiency, particularly to make the aluminacontained in diasporic bauxite soluble, it may be necessary to apply ahigh pressure to the mixture. In a preferred embodiment, the aluminadigester tank is configured to build and maintain a pressure of 1-100bars, 5-90 bars, 10-80 bars, 20-70 bars, 30-60 bars, or 40-50 bars inthe enclosed space, for example, by heating air or gas contained in theenclosed space and/or by pumping (hot) air or gas into the enclosedspace. In a preferred embodiment, the alumina digester tank systemcomprises a pressure detector for detecting the pressure applied to themixture in the enclosed space of the alumina digester tank.

To generate and maintain a high temperature for efficient aluminadigestion in the enclosed space of the alumina digester tank holding themixture of the bauxite and the caustic soda solution, the aluminadigester tank system comprises one or more heaters, e.g. electrical orgas powered heaters, or heat exchangers connected to heat pumps, thatmay be installed on the interior of the top wall, the bottom wall,and/or the side walls and/or in the enclosed space of the aluminadigester tank, for example, by disposing resistive heating elements orheat exchangers or circulating heated air in a network of pipes disposedin the enclosed space. In some embodiments, the heaters are configuredto heat the mixture of the bauxite and the caustic soda solution to atemperature of 60-300° C., 80-300° C., 100-300° C., 100-250° C.,120-200° C., or 150-180° C. In a preferred embodiment, the aluminadigester tank system comprises a temperature detector for detecting thetemperature of the mixture in the enclosed space of the alumina digestertank. In another preferred embodiment, the alumina digester tank systemcomprises a control for operating the at least one heater. The controlis configured to monitor the temperature of the mixture in the enclosedspace of the alumina digester tank, either by communicating with theabove mentioned temperature detector, or by including a temperaturedetector of its own, and to operate the at least one heater when thetemperature of the mixture is below a pre-determined level. As anexample, the control may be a set point thermostat.

The alumina digester tank system comprises one or more outlets disposedon the top wall, the bottom wall, and/or the side walls configured torelease the mixture from the enclosed space of the alumina digestertank. During the digestion, in some instances, the alumina digester tankfunctions as a pressure cooker where the mixture is subjected to a hightemperature and a high pressure. Following the digestion, the mixturemay be preferably transferred to an environment of a lower temperatureand pressure, i.e. a flash tank, before transferred to a settling tankwhere insoluble materials in the mixture, such as sand and iron, settleto the bottom of the settling tank. In a preferred embodiment, theoutlet is connected to a series of “flash tanks” via a pipe. In anotherpreferred embodiment, a second pump is connected to the outletconfigured to pump the mixture out of the enclosed space of the aluminadigester tank via the outlet and into a downstream processing unit, forexample, a flash tank or a series of flash tanks.

In one embodiment, the alumina digester tank system comprises one ormore agitators disposed on the interior of at least one of the top wall,the bottom wall, and the side walls and/or in the enclosed space of thealumina digester tank configured to agitate the mixture in the enclosedspace. The operation of the agitator improves the contact between thebauxite and the caustic soda solution and hence the solubilization ofalumina in the caustic soda solution. The agitator may be a mechanicalmixer comprising a screw or blade turned by a motor, e.g. a blade paddletype impeller disclosed in PERFORMANCE IMPROVEMENT OF ALUMINA DIGESTORS,T. Kumaresan, S. S. Thakre, B, Basu, K. Kaple, H. P. Gupta, A. Bandi, P.Chaturvedi, N. N. Roy, S. N. Gararia, V. Sapra, R. P. Shah, SeventhInternational Conference on CFD in the Minerals and Process Industries,CSIRO, Melbourne, Australia, 9-11 Dec. 2009, incorporated herein byreference in its entirety, or may be a pressurized gas based agitator asdisclosed by U.S. Pat. No. 8,147,117 B2, incorporated herein byreference in its entirety. One such pressurized gas-based agitator ormixer may be obtained from Pulsair (Bellevue, Wash., USA). In apreferred embodiment, a plurality of agitators are disposed throughoutthe entire volume of the mixture in the enclosed space of the aluminadigester tank. For example, a number of mechanical mixers verticallyspaced from one another may be installed on a vertical support beamwhich is disposed in the enclosed space of a verticalcylindrically-shaped alumina digester tank and which spans from the topto the bottom of the mixture.

In one embodiment, the alumina digester tank system comprises one ormore baffles disposed on the interior of at least one of the top wall,the bottom wall, and the side walls and/or in the enclosed space of thealumina digester tank configured to achieve a desired flow pattern ofthe mixture in the enclosed space of the alumina digester tank.Depending on the desired flow pattern of the mixture, the baffles may bein any shape, e.g. a plate shape, a ring shape, a tubular shape, or afunnel shape, and may be placed in any orientation, e.g. horizontal orvertical. The baffles may change the flowing momentum of the mixture andthus affect dispersion level of the mixture, as disclosed in PERFORMANCEIMPROVEMENT OF ALUMINA DIGESTORS, T. Kumaresan, S. S. Thakre, B. Basu,K. Kaple, H. P. Gupta, A. Bandi, P. Chaturvedi, N. N. Roy, S. N.Gararia, V. Sapra, R. P. Shah, Seventh International Conference on CFDin the Minerals and Process Industries, CSIRO, Melbourne, Australia,9-11 Dec. 2009, incorporated herein by reference in its entirety. In apreferred embodiment, a surface of the interior of at least one of thetop wall, the bottom wall, and the side walls of the alumina digestertank, particularly the surface of the interior contacting the mixturecomprising bauxite and a caustic soda solution when the alumina digestertank is in operation, is coated with at least one epoxy resin,preferably using the types of the epoxy resins and the coating methodsto achieve the desirable characteristics of the epoxy resin coatingdescribed above. In some embodiments, the epoxy resin coating covers10-100%, 30-100%, 50-100%, preferably 70-100%, more preferably 90-100%of the interior wall surface, depending on the percentage of theinterior wall surface that comes into contact with the mixture when thealumina digester tank is in operation.

According to a second aspect, the present disclosure relates to analumina digester tank system that includes: (a) an alumina digester tankobtained from a casting or molding of a concrete mix composition in theform of the alumina digester tank and water curing the cast or moldedconcrete mix composition, wherein the alumina digester tank has a heightto diameter ratio of 1-5, 2-4, or 3-4, and comprises a top wall, abottom wall, and side walls defining an enclosed space, wherein theconcrete mix composition comprises: a cementitious blend comprising atleast one hydraulic cement and ground granulated blast furnace slags(GGBFS), wherein a weight percent ratio of at least one hydrauliccement: GGBFS in the cementitious blend lies in the range of (10-50):(50-90), (20-40): (60-80), or (25-35): (65-75) with the sum of theweight percentages of the at least one hydraulic cement and the GGBFSnot exceeding 100%, and water, wherein a weight ratio of the water tothe cementitious blend is 0.2-0.5, 0.3-0.4, or 0.35, and wherein theconcrete mix composition has a content of the cementitious blend of400-550 kg/m³, 400-500 kg/m³, 405-480 kg/m³, 430-470 kg/m³, or 460kg/m³, (b) at least one inlet disposed on at least one of the top wall,the bottom wall, and the side walls of the alumina digester tankconfigured to introduce a mixture comprising bauxite and a caustic sodasolution into the enclosed space of the alumina digester tank, whereinthe alumina digester tank is configured to pressurize the mixture in theenclosed space to 1-100 bars, (c) at least one heater disposed on theinterior of at least one of the top wall, the bottom wall, and the sidewalls and/or in the enclosed space of the alumina digester tankconfigured to heat the mixture to a temperature of 60-300° C., 80-300°C., 100-300° C., 100-250° C., 120-200° C., or 150-180° C., (d) at leastone outlet disposed on at least one of the top wall, the bottom wall,and the side walls of the alumina digester tank configured to releasethe mixture from the enclosed space of the alumina digester tank, (e) atleast one agitator disposed on the interior of at least one of the topwall, the bottom wall, and the side walls and/or in the enclosed spaceof the alumina digester tank configured to agitate the mixture in theenclosed space, (f) a temperature detector for detecting the temperatureof the mixture in the enclosed space of the alumina digester tank, (g) apressure detector for detecting the pressure applied to the mixture inthe enclosed space of the alumina digester tank, and (h) a control foroperating the at least one heater, wherein the control is configured tomonitor the temperature of the mixture in the enclosed space of thealumina digester tank and operate the at least one heater when thetemperature of the mixture is below a pre-determined level.

Like the resultant concrete from the concrete mix composition in thefirst aspect of the present disclosure, the resultant concrete from theconcrete mix composition of this aspect may advantageously exhibit highdurability in a hot and alkaline environment by the presence of a hotcaustic soda solution, as indicated by, for example, a highercompressive strength and a lower chloride permeability relative to aconventional concrete comprising ordinary Portland cement, silica fume,and fly ash but not GGBFS as shown in Examples.

In some embodiments, the cementitious blend in the concrete mixcomposition does not include silica fume (SF), or fly ash (FA), ornatural pozzolan (NP), or any combinations of SF, FA, and NP.

In some embodiments, the alumina digester tank and/or the aluminadigester tank system of this aspect have the same characteristics andfeatures as those described in the first aspect of the presentdisclosure.

In a preferred embodiment, a surface of the interior of at least one ofthe top wall, the bottom wall, and the side walls of the aluminadigester tank, particularly the surface of the interior contacting themixture comprising bauxite and a caustic soda solution when the aluminadigester tank is in operation,is coated with at least one epoxy resin,preferably using the types of the epoxy resins and the coating methodsto achieve the desirable characteristics of the epoxy resin coatingdescribed in the first aspect of the disclosure. In some embodiments,the epoxy resin coating covers 10-100%, 30-100%, 50-100%, preferably70-100%, more preferably 90-100% of the interior wall surface, dependingon the percentage of the interior wall surface that comes into contactwith the mixture when the alumina digester tank is in operation.

In another embodiment, one or more epoxy resins (and their curing agentsif needed) are added to and mixed with the concrete mix composition andthe resulting epoxy resin incorporated concrete mix composition is castor molded in the form of the alumina digester tank. In some embodiments,the types of suitable epoxy resins, the amounts of the epoxy resinsused, and the methods for preparing the epoxy resin incorporatedconcrete mix composition are the same as those described in the firstaspect of the present disclosure. Following water curing of the cast ormolded epoxy resin incorporated concrete mix composition, the resultantconcrete comprises epoxy resin particles dispersed throughout the massof the concrete and may possess improved tensile strength and chemicalresistance.

In some embodiments, the at least one hydraulic cement is at least oneselected from the group consisting of a Portland cement, a calciumaluminate cement, a white cement, a high-alumina cement, a magnesiumsilicate cement, a magnesium oxychloride cement, and an oil well cement.

In a preferred embodiment, the at least one hydraulic cement is aPortland cement. The Portland cement in the cementitious compositionpreferably meets ASTM C150 Type II I/II, III, IV or V requirements orequivalent standard specifications.

In another preferred embodiment, the at least one hydraulic cement is aPortland cement combined with one or more other cements selected from acalcium aluminate cement, a white cement, a high-alumina cement, amagnesium silicate cement, a magnesium oxychloride cement, and an oilwell cement. When the at least one hydraulic cement is a combination ofthe above mentioned cements, the relative weight proportions ofdifferent types of cements may vary without limitation, depending on,for example, the desired content of the cementitious blend in theconcrete mix composition, which is preferably within the rangesdescribed above, the desired compressive strength of the resultantconcrete from the concrete mix composition after a certain period ofcuring of the concrete mix composition with water, and a target hightemperature of the alumina digester tank in operation that the resultantconcrete is expected to withstand while remaining stable, e.g. withoutbreaking or cracking, for a desirable period of time.

Ground-granulated blast-furnace slag (GGBFS) is obtained by quenchingmolten iron slag (a by-product of iron and steel-making) from a blastfurnace in water or steam, to produce a glassy, granular product that isthen dried and ground into a fine powder. The main components of blastfurnace slag are CaO (30-50% or 35-45%), SiO₂ (28-38%, or 30-35%), Al₂O₃(8-24%, 10-20%, or 12-16%), and MgO (1-18%, 5-15%, or 8-12%). Ingeneral, increasing the CaO content of the slag results in increasedslag basicity and an increase in compressive strength. GGBFS reacts likePortland cement when in contact with water. But as the rate of reactionis slower, an activator is necessary. The calcium hydroxide releasedwhen Portland cement reacts with water serves to activate GGBFS, henceGGBFS is preferably combined with Portland cement.

When GGBFS is used in concrete, the resulting hardened cement paste hasmore, smaller gel pores and fewer larger capillary pores than is thecase with concrete made with Ordinary Portland cement. This finer porestructure gives GGBFS concrete a much lower permeability, and makes animportant contribution to the greater durability of this concrete. In apreferred embodiment, the GGBFS meets the standard specification ASTMC989.

In a preferred embodiment, the GGBFS is ground to reach the samefineness as Portland cement in the cementitious blend to obtain asuitable reactivity.

In a preferred embodiment. The GGBFS has a MgO content of 10-18%,12-16%, or 14%, and/or a Al₂O₃ content of 10-24%, 12-20%, or 14% toprovide a maximal compressive strength.

In some embodiments, the concrete mix composition further comprisesaggregates, reinforcing materials, and/or high range water reducers,with their respective types, characteristics, and amount ranges beingthe same as those described in the first aspect of the presentdisclosure.

In some embodiments, die at least one hydraulic cement in the concretemix composition is a Portland cement and, after the concrete mixcomposition is cured with water for at least 1 month, at least 2 months,or at least 3 months, the water cured product of the concrete mixcomposition has a compressive strength of 55-120 MPa , 60-110 MPa, or65-100 MPa.

In some embodiments, the at least one hydraulic cement in the concretemix composition is a Portland cement and, after the concrete mixcomposition is cured with water for at least 1 month, at least 2 months,or at least 3 months, the water cured product of the concrete mixcomposition has a reduction in compressive strength of 2-15%, 3-10%, or6-8% when exposed to an alkaline solution comprising 10-50%, 15-45%,20-40%, or 25-35% of one or more alkali hydroxides (i.e. LiOH, NaOH,KOH, RbOH, and CsOH) at 40-80° C., 50-70° C., or 60° C. for 4-16 months,6-14 months, 8-12 months, or 10 months as compared to the water curedproduct of the concrete mix composition exposed to water at 15-35° C.,20-30° C., or 25° C. for the same length of time.

In some embodiments, the at least one hydraulic cement in the concretemix composition is a Portland cement and, after the concrete mixcomposition is cured with water for at least 1 month, at least 2 months,or at least 3 months, the water cured product of the concrete mixcomposition has a weight loss of 0-6%, 0-4%, 0-2%, 0-1%, or 0-0.8% whenexposed to an alkaline solution comprising 10-50%, 15-45%, 20-40%, or25-35% of one or more alkali hydroxides (i.e. LiOH, NaOH, KOH, RbOH, andCsOH) at 40-80° C., 50-70° C., or 60° C. for 4-16 months, 6-14 months,8-12 months, or 10 months as compared to the water cured product of theconcrete mix composition exposed to water at 15-35° C., 20-30° C., or25° C. for the same length of time.

In some embodiments, the at least one hydraulic cement in the concretemix composition is a Portland cement and, after the concrete mixcomposition is cured with water for at least 1 month, at least 2 months,or at least 3 months, the water cured product of the concrete mixcomposition has a chloride permeability of 1000-3000, 1500-2800,1800-2600, or 2000-2500 Coulombs when exposed to an alkaline solutioncomprising 10-50%, 15-45%, 20-40%, or 25-35% of one or more alkalihydroxides (i.e. LiOH, NaOH, KOH, RbOH, and CsOH) at 40-80° C., 50-70°C., or 60° C. for 8-20 months, 10-18 months, 12-16 months, or 13-15months.

In some embodiments, the at least one hydraulic cement in the concretemix composition is a Portland cement and, after the concrete mixcomposition is cured with water for at least 1 month, at least 2 months,or at least 3 months, the water cured product of the concrete mixcomposition has an expansion of 200-1200 microns, 250-1100 microns,300-1000 microns, 400-900 microns, 500-800 microns, or 600-700 micronswhen exposed to an alkaline solution comprising 10-50%, 15-45%, 20-40%,or 25-35% of one or more alkali hydroxides (i.e. LiOH, NaOH, KOH, RbOH,and CsOH) at 40-80° C., 50-70° C., or 60° C. for 4-16 months, 6-14months, 8-12 months, or 10 months.

In some embodiments, the resultant concretes from the embodiments of theconcrete mix composition have a void content of less than 15% by volume,preferably less than 10% by volume, or more preferably less than 5% byvolume.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLE 1 Concrete Mix Specimen Preparation

Concrete mix specimens were prepared with three types of cementitiousmaterial mixtures, namely, M1: Ordinary Portland cement (OPC)+silicafume (SF)+fly ash (FA); M3: Ordinary Portland cement (OPC)+groundgranulated blast furnace slag (GGBFS); and M4: Ordinary Portland cement(OPC)+silica fume (SF)+natural pozzolan (NP). The natural pozzolan usedcomprised the powdered form of volcanic rock abundantly available on RedSea coast in the Western region of Saudi Arabia. The properties of thisnatural pozzolan are similar to those of NP available in the many otherparts of the world. An additional concrete mix specimen M2 was preparedwith Ordinary Portland cement (OPC) and the specimen was coated twicewith an epoxy resin to form two epoxy resin coatings, with each epoxyresin coating having a thickness of 200 microns. All of the concrete mixspecimens were prepared with a combined cementitious materials contentof 460 kg m³ and a water to cementitious materials ratio in the range of0.305 to 0.35. Table 1 shows the contents of the cementitious materialsin the four concrete mix specimens.

TABLE 1 Details of concrete mix specimens prepared for exposure to waterand caustic soda solution. Mix OPC SF FA GGBFS NP Mix # constituentsw/cm kg/m³ kg/m³ kg/m³ kg/m³ kg/m³ Remarks M1 OPC + SF + FA 0.305 255 45160 — — Cast on site (Currently Used) M2 OPC + epoxy 0.35 460 — — — —Epoxy coated. coating M3 OPC + GGBFS 0.35 138 — — 322 — Developed in theLab M4 OPC + SF + NP 0.35 255 45 — — 160 Developed in the Lab Notation:OPC: Ordinary Portland cement; SF: Silica fume; FA: Fly ash; GGBFS:Ground granulated blast furnace slag; NP: Natural pozzolan; w/cm: waterto cementitious materials ratio.

EXAMPLE 2 Exposure of the Concrete Mix Specimens to Water and a CausticSoda Solution

After three months of curing, the specimens were divided into twogroups. One group was exposed to water under a controlled temperature of23±2° C. while the second group of the specimens was exposed to acaustic soda solution containing 320 g/L of NaOH and maintained at 60°C.

EXAMPLE 3 Evaluation of the Concrete Mix Specimens Following theExposure to Water and the Caustic Soda Solution

The performance of die four concrete mix specimens exposed to thecaustic soda solution was evaluated by visual examination, and bydetermining the compressive strength, expansion, resistance to chlorideion penetration and weight loss. The test details, specimen geometry,and test duration are provided in Table 2.

TABLE 2 Details of the geometry of the concrete mix specimens, tests andtest durations Specimen Test description/standard geometry Test durationVisual examination Cylinder with After 4, 8, 12 and 16 Compressivestrength (ASTM C39) a diameter of months of exposure. 75 mm and a heightof 150 mm Length change/Expansion (ASTM 40 × 40 × 160 mm Periodicmeasurement up C157) prism to 16 months of exposure. Resistance tochloride ion penetration Cylinder with Before exposure and after (ASTMC1202) a diameter of completion of exposure for 75 mm and a 12 and 16months. height of 150 mm Pulse velocity (ASTM C597) Cylinder with After4, 8, 12 and 16 a diameter of months of exposure. 75 mm and a height of150 mm

1. Visual Observations:

The condition of the concrete mix specimens exposed to water and thecaustic soda solution for 16 months is shown in FIGS. 1A-4B. Maximumdeterioration was noted in the specimens prepared with OPC+SF+FA (i.e.M1, reference concrete mix specimen). The two concrete mix specimens M3and M4 developed in this disclosure did not exhibit any deterioration.Minor debonding of the epoxy resin coating was noted on the epoxy resincoated specimens M2.

2. Compressive Strength:

The development of compressive strength in the four concrete mixspecimens cured under water for three months is depicted in FIG. 5. Thecompressive strength increased with time in all of the concrete mixspecimens. After three months of curing, the concrete mix specimen M3(OPC+GGBFS) exhibited the highest compressive strength of more than 65MPa, while the concrete mix specimen M2 (OPC coated with an epoxy resin)exhibited the lowest compressive strength of 52 MPa. The compressivestrength of the concrete mix specimens M3 and M4 was more than that ofM2 and the reference concrete mix specimen M1.

The reduction in the compressive strength due to exposure to the causticsoda solution is depicted in FIG. 6. The maximum reduction of about 25%in compressive strength was noted in concrete mix specimen M1 (referenceconcrete mix specimen) after 16 months of exposure to the caustic sodasolution. By contrast, the reduction in compressive strength in theother three concrete mix specimens was around 10% after 16 months ofexposure to the caustic soda solution.

3. Weight Loss:

The weight loss in the concrete mix specimens exposed to the causticsoda solution maintained at a high temperature of 60° C. is depicted inFIG. 7. The maximum weight loss of 9.03% was noted in concrete mixspecimen M1 (reference concrete mix specimen) following a 16-monthexposure. The weight loss in the other three concrete mix specimens wasin the range of 1.26-2.43% following a 16-month exposure.

4. Chloride Permeability:

The chloride permeability in the concrete mix specimens exposed to thecaustic soda solution is depicted in FIG. 8. The chloride permeabilityincreased with the time of exposure to the caustic soda solution in allof the concrete mix specimens. The increase in the chloride permeabilityis indicative of a loss in the durability of the concrete mix specimens.The chloride permeability in concrete mix specimen M1 (referenceconcrete mix specimen) was more than that in the other three concretemix specimens following a 16-month exposure. While the chloridepermeability in concrete mix specimen M1 exposed to the caustic sodasolution for 16 months was 3,132 Coulombs, it was in the range of1,795-2,705 Coulombs in the other three concrete mix specimens after 16months of exposure to the caustic soda solution.

5. Expansion:

The expansion of concrete mix specimens M1-M4 following the exposure tothe caustic soda solution for various periods of time is depicted inFIG. 9. As expected, the expansion increased with time in all of theconcrete mix specimens M1-M4. After 16 months of exposure to the causticsoda solution, concrete mix M1 displayed an expansion of 2,369 micronswhile concrete mixes M2, M3, and M4 had an expansion of 835, 967, and740 microns, respectively.

1. A cementitious blend composition, comprising: at least one hydrauliccement, silica fume (SF), and natural pozzolan (NP), wherein a weightpercent ratio of at least one hydraulic cement: SF:NP in thecementitious blend composition lies in the range of (24-63): (5-44):(32-40) with the sum of the weight percentages of the at least onehydraulic cement, the SF, and the NP not exceeding 100%.
 2. Thecementitious blend composition of claim 1, wherein the at least onehydraulic cement is at least one selected from the group consisting of aPortland cement, a calcium aluminate cement, a white cement, ahigh-alumina cement, a magnesium silicate cement, a magnesiumoxychloride cement, and an oil well cement
 3. The cementitious blendcomposition of claim 1, wherein the natural pozzolan (NP) is at leastone selected from the group consisting of metakaolin, calcined shale,calcined clay, volcanic glass, zeolitic trass or tuffs, rice husk ash,Diatomaceous earth, and calcined shale.
 4. A concrete mix compositioncomprising water and the cementitious blend composition of claim 1,wherein a weight ratio of the water to the cementitious blendcomposition is 0.2-0.5, and wherein the concrete mix composition has acontent of the cementitious blend composition of 400-550 kg/m³.
 5. Theconcrete mix composition of claim 4, further comprising at least onereinforcing material selected from the group consisting of steel rebar,wire mesh, steel fibers, polypropylene fibers, nylon fibers, andpolyvinyl alcohol fibers.
 6. The concrete mix composition of claim 4,further comprising at least one high range water reducer.
 7. Theconcrete mix composition of claim 6, wherein the at least one high rangewater reducer is a polycarboxylate superplasticizer or a naphthalenehigh range water reducer.
 8. The concrete mix composition of claim 4,further comprising at least one aggregate selected from the groupconsisting of fused aluminum oxide (FAO), calcined bauxite, and emery.9. The concrete mix composition of claim 8, wherein the at least oneaggregate comprises fused aluminum oxide (FAO) at 50-100% of the totalvolume of the at least one aggregate.
 10. The concrete mix compositionof claim 4, wherein the at least one hydraulic cement is a Portlandcement.
 11. A water cured product of the concrete mix composition ofclaim 10, wherein the water cured product has a compressive strength of60-90 MPa.
 12. A water cured product of the concrete mix composition ofclaim 10, wherein the water cured product has a reduction in compressivestrength of 2-15% when exposed to an alkaline solution comprising 10-50%of one or more alkali hydroxides at 40-80° C. for 4-16 months ascompared to the water cured product exposed to water at 15-35° C. forthe same length of time.
 13. A water cured product of the concrete mixcomposition of claim 10, wherein the water cured product has a weightloss of 0-6% when exposed to an alkaline solution comprising 10-50% ofone or more alkali hydroxides at 40-80° C. for 4-16 months as comparedto the water cured product exposed to water at 15-35° C. for the samelength of time.
 14. A water cured product of the concrete mixcomposition of claim 10, wherein the water cured product has a chloridepermeability of 1200-2000 Coulombs when exposed to an alkaline solutioncomprising 10-50% of one or more alkali hydroxides at 40-80° C. for12-16 months.
 15. A water cured product of the concrete mix compositionof claim 10, wherein the water cured product has an expansion of 200-850microns when exposed to an alkaline solution comprising 10-50% of one ormore alkali hydroxides at 40-80° C. for 4-16 months.
 16. An aluminadigester tank system, comprising: (a) an alumina digester tank obtainedfrom a casting or molding of the concrete mix composition of claim 4 inthe form of the alumina digester tank and water curing the cast ormolded concrete mix composition, wherein the alumina digester tank has aheight to diameter ratio of 1-5 and comprises a top wall, a bottom wall,and side walls defining an enclosed space, (b) at least one inletdisposed on at least one of the top wall, the bottom wall, and the sidewalls of the alumina digester tank configured to introduce a mixturecomprising bauxite and a caustic soda solution into the enclosed spaceof the alumina digester tank, wherein the alumina digester tank isconfigured to pressurize the mixture in the enclosed space to 1-100bars, (c) at least one heater disposed on the interior of at least oneof the top wall, the bottom wall, and the side walls and/or in theenclosed space of the alumina digester tank configured to heat themixture to a temperature of 60-300° C., (d) at least one outlet disposedon at least one of the top wall, the bottom wall, and the side wallsconfigured to release the mixture from the enclosed space of the aluminadigester tank, (e) at least one agitator disposed on the interior of atleast one of the top all, the bottom wall, and the side walls and/or inthe enclosed space of the alumina digester tank configured to agitatethe mixture in the enclosed space, (f) a temperature detector fordetecting the temperature of the mixture in the enclosed space of thealumina digester tank, (g) a pressure detector for detecting thepressure applied to the mixture e enclosed space of the alumina digestertank, and (h) a control for operating the at least one heater, whereinthe control is configured to monitor the temperature of the mixture inthe enclosed space of the alumina digester tank and operate the at leastone heater when the temperature of the mixture is below a pre-determinedlevel.
 17. The alumina digester tank system of claim 16, furthercomprising: at least one first pump connected to the at least one inletconfigured to pump the mixture into the enclosed space of the aluminadigester tank via the at least one inlet, at least one second pumpconnected to the at least one outlet configured to pump the mixture outof the enclosed space of the alumina digester tank via the at least oneoutlet, and at least one baffle disposed on the interior of at least oneof the top wall, the bottom wall, and the side walls and/or in theenclosed space of the alumina digester tank configured to achieve adesired flow pattern of the mixture in the enclosed space of the aluminadigester tank.
 18. The alumina digester tank system of claim 16, whereina surface of the interior of at least one of the top wall, the bottomwall, and the side walls of the alumina digester tank is coated with atleast one epoxy resin.
 19. An alumina digester tank system, comprising:(a) an alumina digester tank obtained from a casting or molding of aconcrete mix composition in the form of the alumina digester tank andwater curing the cast or molded concrete mix composition, wherein thealumina digester tank has a height to diameter ratio of 1-5 andcomprises a top wall, a bottom wall, and side walls defining an enclosedspace, wherein the concrete mix composition comprises: a cementitiousblend comprising at east one hydraulic cement and ground granulatedblast furnace slags (GGBFS), wherein a weight percent ratio of at leastone hydraulic cement: GGBFS in the cementitious blend lies in the rangeof (10-50): (50-90) with the sum of the weight percentages of the atleast one hydraulic cement and the GGBFS not exceeding 100%, and water,wherein a weight ratio of the water to the cementitious blend is0.2-0.5, and wherein the concrete mix composition has a content of thecementitious blend of 400-550 kg/m³, (b) at least one inlet disposed onat least one of the top wall, the bottom wall, and the side walls of thealumina digester tank configured to introduce a mixture comprisingbauxite and a caustic soda solution into the enclosed space of thealumina digester tank, wherein the alumina digester tank is configuredto pressurize the mixture in the enclosed space to 1-100 bars, (c) atleast one heater disposed on the interior of at least one of the topwall, the bottom wall, and the side walls and/or in the enclosed spaceof the alumina digester tank configured to heat the mixture to atemperature of 60-300° C., (d) at least one outlet disposed on at leastone of the top wall, the bottom wall, and the side walls of the aluminadigester tank configured to release the mixture from the enclosed spaceof the alumina digester tank, (e) at least one agitator disposed on theinterior of at least one of the top wall, the bottom wall, and the sidewalls and/or in the enclosed space of the alumina digester tankconfigured to agitate the mixture in the enclosed space, (f) atemperature detector for detecting the temperature of the mixture in theenclosed space of the alumina digester tank, (g) a pressure detector fordetecting the pressure applied to the mixture in the enclosed space ofthe alumina digester tank, and (h) a control for operating the at leastone heater, wherein the control is configured to monitor the temperatureof the mixture in the enclosed space of the alumina digester tank andoperate the at least one heater when the temperature of the mixture isbelow a pre-determined level.
 20. The alumina digester tank system ofclaim 19, wherein a surface of the interior of at least one of the topwall, the bottom wall, and the side walls of the alumina digester tankis coated with at least one epoxy resin.